IBM opens bandgap for graphene

PORTLAND, Ore. — IBM Research says it has opened a bandgap for carbon-based graphene field-effect transistors (FETs), removing one of the last roadblocks to commercialization of the technology. By utilizing a dual-gate, bi-layer architecture, IBM said it demonstrated a graphene FET that could someday rival complementary metal oxide semiconductor.

"Graphene doesn't naturally have a bandgap, which is necessary for most electronic applications," said IBM Fellow Phaedon Avouris, who oversees the company's carbon-based materials efforts. "But now we can report tunable electrical bandgaps of up to 130meV for our bi-layer graphene FETs. And larger bandgaps are certainly feasible."

According to Avouris, this opens the possibility of future applications for graphene in digital electronics and in optoelectronics devices such as photodetectors, imaging and others.

Graphene has higher carrier mobility than silicon, but has been hampered by the lack of a band gap, which has kept the on-off ratio of graphene transistors dismally low—usually less than 10 compared to hundreds for silicon. But thanks to the dual-gate, bi-layer architecture of IBM's current graphene FET prototype, the company said it was able to attain an on-off current ratio of around 100 at room temperature and 2,000 when the device was cooled.

The key to advancement was insulating the high-k gate dielectric from the graphene transistor channel by a polymer. IBM had previously reported lowering the noise level of graphene FETs using a bi-layer architecture, but this is the first time it reported insulating the graphene channel from its high-k gate dielectric with a polymer. The polymer reportedly reduced electron scattering that is ordinarily caused by charged impurities in oxides that directly contact graphene, thereby boosting the FET's on-off current ratio.

Next, IBM plans to begin optimizing its design by scaling down the thickness of its insulating layers in order to achieve even higher electric fields, to open a wider band gap, and to further improve the on-off current ratios of graphene FETs.